If it's anything like a standard 3-pin fan connector then you have your 12 V, your Ground and your fan speed back (don't know what a pump normally reports back). The 4th pin would be to control it yourself (PWM pin) without volt modding (lowering the voltage to your fan/pump) yourself.

I'm pretty sure that the 3 pin is just for your cpu fan header if your board needs to have a fan plugged into it in order to boot. It will also report an rpm to the bios - I'd guess its the speed of the h80's pump.